Catch-in-Focus Tutorial

Snapping photos as soon as your subject gets in focus

Catch-in focus is a powerful technique that allows DSLRs to use information from the autofocus system to confirm focus even when using manual lenses. What's more, with this technique the camera will automatically take a picture once your subject comes into focus! Easy to learn and master, catch-in focus can be a life-saver in some situations.

Sample hummingbird photo taken using catch-in-focus

Read on to learn how to use catch-in focus effectively.

Pentax users are lucky to be able to use any K-mount lens ever made on their digital cameras. However, for some photographers accustomed to automatic modes and autofocus, using a manual lens can be a daunting challenge.

Luckily, it is possible to use part of the camera’s autofocus system even with a fully manual lens. The same applies to autofocus lenses offering an AF/MF switch. This technique, called “catch-in-focus” or “focus trap", is easy to use once you know how it works.

This article presents the ins and outs of catch-in focus. We will start by showing how to activate this function, followed by a step-by-step guide to use the technique and some examples of possible uses.

Activating Catch-in-Focus

The exact menu setting to activate catch-in focus can vary slightly from one camera to the next. It is always enabled by setting the appropriate Custom Function. The following table summarizes the custom item number for some recent camera models.

Camera model

Custom item number

K20D

34

K-7

35

K-5 / K-5 II

25

K-3 / K-3 II

25

K-1

24

K-30 / K-50

20

K-S1

24

K-S2

26

Older cameras such as the K10D often refered to catch-in focus as trap focus. With the K10D there is no menu setting, catch-in focus is always active as long as the lens has a bare metal mount (such as a K or M mount lens).

If applicable on your camera model, also make sure that the shutter priority for AF.S is set to “Focus priority” (custom menu item #15 or #17 on many cameras, called "AF.S Setting" and enabled by default).

Once this is done, a manual lens needs to be mounted on the camera.

Alternatively, you can use an autofocus lens with an AF/MF switch. The switch should be set to MF.

If your AF lens doesn't have such a switch, the camera can also be tricked into thinking that a manual lens is mounted by depressing the lens lock button or even taping over the electrical contacts, though this is far from recommended!

Users who have set the AF to trigger only via the rear AF button will not be able to use catch-in focus unless they also allow AF via the shutter button.

Using Catch-in-Focus

Just a few easy steps will let you take pictures using catch-in focus.

Set your camera to AF mode

Set the camera to AF.S (set via the AF switch or the menu, depending on your body)

Select the AF point(s) you'd like to use*

Focus at your desired distance

Fully press and hold the shutter button, and wait for your subject to come in focus. When it does, the camera will automatically take the picture**

As with any manual focus operation, you will see a confirmation in the viewfinder when focus is achieved: the red focus point and the green focus hexagon at the bottom will light up.

The main challenge is to actually set the focus distance. It is possible to use the distance scale engraved on many lenses. This will work best for longer depths of field, which will be more tolerant to small imprecisions. Methods to set the focus will vary depending on the application.

Center AF point

*Note that manual focus lenses will only support use of the center AF point. We recommend using the center AF point regardless as it is more sensitive than the others on certain bodies, and it is easier to compose with due to the presence of markings in the center of the viewfinder.

**It is possible and oftentimes necessary to use a wired remote with a lock function to effectively keep the shutter depressed without physically leaving a finger on the shutter button.

Examples of Useful Applications

Here is a short list presenting a few examples of potential uses for catch-in focus.

Macro photography with moving subjects, such as leaves in the wind. Roughly lock the focus, set a fast shutter speed to freeze movement, and wait for your subject to become sharp.

Moving vehicles, for instance racecars on a track. Focus on the ground where you expect the car to pass, and wait for it!

In a studio, set the focus and move slowly towards or away from your subject. The camera will snap the image when the face is in focus.

Birds on a manger. Focus and be patient…

To lock focus on a difficult subject, press and hold the shutter and slowly move the focus ring. The camera will take the picture when the focus distance is optimal.

In short, anything with predictable action can be photographed by using catch-in focus. Just remember that there are tolenrances in the AF system, so we recommend using narrower apertures whenever possible to increase the depth of field.

Catch-in focus is a simple but very effective technique. Don't hesitate to share your favorite uses in the comments!

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About The Authorbdery

I am an optical designer working in the photonics industry. I also hold a PhD in physics, specialized in optics. During the course of my education, I have studied lens design, atmospheric light... More articles by bdery →

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